Technical Note on Using the Movement Velocity to Estimate the Relative Load in Resistance Exercises – Response

Abstract

Dear Editor, Thank you for the opportunity to respond to the point s raised by Naclerio & Larumbe-Zabala regarding our recent article [5] in Sports Medicine International Open. This study provided a detailed description of the load-velocity relationship in the full back squat exercise along with the novel and very important applications that can be derived from this relationship for the practice of resistance exercise. We are pleased that our data have provided stimulus for further inquiry. However, we would like to point out that most of the criticisms expressed by Naclerio & Larumbe-Za-bala in their Letter to the Editor are directed towards an article published in 2010 in another scientific journal [1] which analyzed the bench press exercise, and not to the present study which involved the back squat. However, since both studies are related in many ways and they form the basis of the velocity-based resistance training line of research pioneered by our group and developed over the last two decades, we are happy to address their concerns. In their letter, the authors stated that the data analyses that we performed were not correct and could lead to an overestimation of the relative load. Had the authors taken the time to compare the estimations of relative load (percentage of one-repetition maximum, % 1RM) from mean velocity (MV) data obtained when using the equations provided by us (Load = 7.5786 MV 2 − 75.865 MV + 113.02) [1] and them (Load = 107.75 − 62.97 MV) [3] for the bench press exercise, they could have easily verified that no such overestimation exists. Thus, for instance, when comparing the relative loads corresponding to MV values within a range of 1.15 to 0.20 m · s − 1 (~35-98 % 1RM), and calculating the loads for each 0.05 m · s − 1 change in MV, an almost negligible mean difference of 0.65 % 1RM exists when using our equation compared to theirs, with a minimum difference of − 0.22 % 1RM (for 0.85 m · s − 1) and a maximum difference of 2.99 % 1RM (for 0.20 m · s − 1). Our analyses cannot be so wrong when the correlation between the loads obtained using the aforementioned two equations is r = 0.9995 within a velocity range of 1.15 to 0.18 m · s − 1. Interestingly , this very analysis further seems to indicate that our quadratic equation does, in fact, better fit the obtained load-velocity data points. In our study [1], actual mean velocity attained with the 1RM load (V 1RM) was 0.16 ± 0.04 m · s − 1 whereas it was very similar, although somewhat more variable (0.162 ± 0.07 m · s − 1 for men), in the Nacler-io & Larumbe-Zabala study [3]. When using their equation to estimate load from this MV value of 0.16 m · s − 1 , a load of 97.6 % 1RM is obtained, whereas a load of 100.9 % 1RM results when using ours. This indicates that their equation [3] to estimate relative load from MV does indeed deviate from the actual measured value (which it tends to slightly underestimate) more than our original equation [1], especially for the slowest velocities (MV ≤ 0.20-0.25 m · s − 1), i. e. those corresponding to the heaviest loads (≥ 95 % 1RM). Consequently, this recent equation [3] appears to offer little, if any, additional value compared to that published by us seven years ago [1]. In our original study [1], 56 out of the 120 well-trained men who made up the total sample performed the progressive loading test in the bench press exercise twice, being assessed on a second occasion following a period of 6 weeks of resistance training. The load (% 1RM)-velocity data from these two tests from each subject were intentionally added to the total sample after verifying that the obtained load-velocity equations were almost identical when considering the data derived from the 120 subjects or the 176 tests as the data sample. In this regard, the caption of Figure 1 of that study [1] clearly indicates that 176 tests (not subjects) were included. The equation obtained when only considering the first test performed by each subject (n = 120) is now provided for anyone wishing to check the obtained findings: MPV = − 0.00003233 Load 2-0.02022 Load + 1.881 (R 2 = 0.980; SEE = 0.060 m · s − 1 ; N = 1045) where MPV corresponds to the mean pro-pulsive velocity value [6] and Load is expressed as the percentage of 1RM. The obtained MPV values for each load between 30 and 100 % 1RM obtained when using the above provided equation compared to the original equation [1] differ between 0 and 0.003 m · s − 1 (three thou-sandths of a meter per second!). In addition , as it can be observed, the coefficient of determination (R 2), an indicator of the goodness of the fit, remains at 0.98. Thus, the inclusion of those 56 additional tests did not result in R 2 being inflated as Nacler-io & Larumbe-Zabala have suggested in their letter. In this particular regard, the references [2,7] provided by the authors are not pertinent to this question since we have only measured one variable and we are not using a multiple regression analysis. Further evidence for the validity of our findings comes from another published study of our research group [4] where the velocity-and power-load relationships of the bench press and prone bench pull exercises were compared in a different sample of 75 men. The obtained load-velocity equation (R 2 = 0.97) was provided in Figure 2 of that study [4]. When again comparing the results of applying this equation [4] to those of the original one [1], within a 30-100 % 1RM load range, the maximum difference for any given percentage of 1RM is 0.01 m · s − 1. In our recent study analyzing the load-velocity relationship of the squat exercise [5], it is clearly explained and discussed (see Table 2 and Figure 3 of the article) that when data from the total sample (n = 80) is divided into subgroups of significantly different relative strength performance (1RM/ body mass)-something that had already been done in our original article [1]-, no differences were found for the velocity attained against each percentage of 1RM,